New fuelling strategies for port injected spark ignition engine towards improvement in fuel consumption and exhaust emission.

Multi-point fuel injection (port injection) became popular with most passenger cars as it eliminated most fuel transportation problems through the induction system hence providing better fuel distribution, fuel consumption and less exhaust emission. However, fuel deposition on the inlet port wall and on the valve stem and shoulder, in particular, during transient and low speed running forced many car manufacturers to investigate other fuel injection techniques as alternatives. This paper reports on an effort towards improving port injection performance employing two and three-dimensional computer modelling studies for air flow and fuel spray behaviour for port injected engine. Further Computational Fluid Dynamics (CFD) simulations employing FLUENT software were carried out for direct injection based on the internal dimensions of a WIRA 1.6 L engine. A Laser Imaging System is used to investigate the fuel spray development in terms of the spray angle, spray penetration and the radial axis. The fuel spray characteristics in terms of the two components of fuel droplet velocities and the fuel droplet diameters were studied using the Particle Dynamic Analyser (PDA) system. Fuel spray generated from a fuel injector was used in the experimental investigation. The fuel injector used was from the fuelling system of a WIRA 1.6L engine with modifications for an extension. It was found that the spray angle stays at 36.8 degrees at all engine speeds. This is because the fuel pressure at the nozzle inlet (at the main trial) is constant. Results reveal that droplet diameter is in the range of 65 microns to 80 microns. The diameter of droplets also showed a tendency to increase with higher engine speed. Another specific objective of the project is to employ Computational Fluid Dynamic (CFD) simulations in the study of fuel transportation and mixing behaviour in port-injected engines. This was subsequently extended to simulations of direct injection into the combustion chamber. Various designs of a modified combustion chamber and a suitable piston head shape to suit direct injection operations are reported. A study, at different engine speeds, of spray locations and fuel injection angles were conducted. The maximum air velocity was found to be at the exit of the air inlet valve. Two highly turbulent domains were observed on both sides on the inlet valve and a stagnation domain below the valve face note. The spray angle has to be off- setted by about 30 degrees relative to the valve stem axis in order to give significant spray distribution in the cylinder.